The present invention relates generally to electromagnetic control devices, such as relays, solenoids, clutches and brakes and more particularly to a class of these devices wherein it is desired to "FORCE" the operation of the device so as to obtain rapid travel and overcome high inertial and spring loading.
It is common practice in the industry to provide the desired forcing action by generating a magnetic force that is substantially greater than required to marginally actuate the device or to maintain the device in an actuated state. This practice is acceptable in applications that require only a short or intermittent duty cycle where heat generated by such over-energizing is not deleterious to the life or operation of the device. When continuous duty is required, various switching arrangements have been used to connect an additional resistance or coil winding in such a way that additional force is obtained only when the device is initially energized and the magnetic force is thereafter reduced to a level sufficient to maintain the device energized but is within the continuous duty ratings of the device.
All of the prior art relating to this problem have a similar deficiency in that the additional coil or winding is only used for a portion of the operation. Some coils or windings are used only during pull-in and others are used only after pull-in has occurred. This obvious inefficiency is costly in terms of money, complexity, energy, size and weight.
Illustrative of the manner in which a number of inventors have attempted to solve existing problems may be found in U.S. Pat. Nos. 2,457,017; 2,540,022; and 2,951,189. In U.S. Pat. No. 2,457,017 to Walley, there is disclosed mechanical structure that emphasizes the advantages of high contact pressure, sensitivity and shock resistance due to the lightweight of the contacts. Electrically, it places a second winding in series with the main winding to reduce the current and power.
U.S. Pat. No. 2,540,002 to Rabenda discloses and teaches the use of two coils in PICK-UP & HOLD. Rabenda addresses the problem where many of these relays are used in close proximity; i.e., adding machines, etc. Each coil then acts as a miniature transformer and couples to the adjacent coils to alter their pick-up and release characteristics.
U.S. Pat. No. 2,951,189 to Hajny shows and teaches motor principles to cause rotation of a crank and thus operation of a valve. The rotary motion is also used to cause a switching action through a slip ring and contact arrangement to connect or disconnect a second coil in series with the pick-up. There are shown two switching arrangements. One shorts a coil out of the circuit and the other switches a coil into the circuit.